Recently, moldable plastic materials of improved mechanical properties have been molded into component parts which have increasingly replaced heavier metal components in a myriad of commercial goods and applications. Among the most important and widely used engineering plastics are thermoplastic materials of which polyamides, i.e. nylon, polyesters, i.e polyalkylene terephthalates, and wholly aromatic polyesters such as formed by reaction of aromatic dicarboxylic acids with bisphenols can be mentioned.
It is well known that engineering plastics may be filled with inorganic fillers and other substances to form uniform compositions. Reinforcing fillers of various sizes, shapes and amounts have been incorporated into plastics for a variety of purposes, which include opacification and coloration, increase in abrasion resistance, modification of thermal expansion and conductivity, improvements in mechanical properties such as tensile and flexural properties. However, in general, the addition of even minor amounts of these fillers to moldable plastics has often had a deleterious effect on the impact strength of the moldable plastic. Moreover, high filler loadings have adversely affected other physical and mechanical properties as well.
Attempts have been made to enhance the mechanical properties of filled plastic compositions. For example, coupling agents have been added to the filled plastic compositions in order to more readily adhere the filler to the polymer or aid in dispersing the filler uniformly in the polymer matrix. Among patents which disclose the addition of coupling agents to filled engineering plastic compositions include U.S. Pat. Nos. 3,290,165; 3,419,517; 3,833,534; and 4,528,303.
While filled engineering plastic compositions containing coupling agents can be compounded to exhibit a high modulus of elasticity, strength, and heat distortion temperature, it is always desirable to improve the performance level of any composition. In the case of the filled thermoplastic nylon or polyester compositions, for example, one area where improvement is particularly desirable is still in the area of impact strength and, in particular, multiaxial impact strength such as "falling weight impact" which is a modified, and often better, indication of "on the job" performance than the uniaxial impact strength measured by Izod impact.
It is known that the impact strength of filled plastic compositions may be increased by such methods as the incorporation of an impact modifier in the plastic phase or, filled plastic compostions with improved impact may be formulated by selecting for use polymers which have inherent impact strength. However, the improvement in impact strength thus obtained for any given plastic composition is inevitably obtained at the expense of a decrease in other important mechanical properties such as the modulus of elasticity. Attempts have been made to overcome such deficiency, for example, as disclosed in U.S. Pat. No. 4,399,246 wherein a filled polyamide composition of improved falling weight impact resistance has incorporated therein an aminofunctional silane coupling agent and an N-substituted hydrocarbonyl sulfonamide. Because of the typical variable compounding capacity of engineering plastic compositions, it is possible to extend the useful range of application of these compositions by tailoring them to suit a particular use. For example, filled prior art compositions ranging from those for applications requiring moderate impact strength but not a high modulus of elasticity, to those for applications requiring high modulus but for which good impact strength is not necessary, may be formulated by the inclusion or exclusion of impact modifier, the increase or decrease in the amount of filler, and the proper selection of the matrix polymer. It should be recognized, however, that although this ease of "tailoring" prior art compositions to the requirements of a particular application is a fortunate advantage, it is basically a property-balancing compromise indicating a need for higher performance materials with the cost and fabrication advantages of the prior art filled polymer compositions.
As previously mentioned, treated fillers or, in particular, fillers coated or mixed with coupling agents have been incorporated into moldable plastics to enhance the mechanical properties of the molded composites. There is a large quantity of art related to modifying the physical and mechanical properties of molded plastic compositions by altering the surface of fillers by chemical treatment such as by providing a coating thereon and incorporating such coated fillers into the moldable plastic matrix. The present invention is concerned with and the primary object thereof is improving the mechanical properties, in particular, the impact strength of filled plastic compositions without unduly sacrificing the other mechanical properties by incorporating therein a novel treated filler. Another object is to provide a novel treated filler and method of making same.
These as well as other objects and aspects of the invention will become clear to those of ordinary skill in the art upon consideration of the foregoing specification and appended claims.